1. Field of the Invention
This invention relates to a bending device, usually referred to in the glass bending art as a bending iron, for shaping glass for use in aircraft transparencies, and more particularly relates to a bending iron for symmetric/asymmetric shaping of glass sheets cut to size for use in the manufacture of monolithic and/or laminated aircraft transparencies.
2. Presently Available Bending Device Technology
Bending devices, commonly referred to in the bending art as Pending irons, are well known for shaping glass sheets for use in the manufacture of monolithic and laminated transparencies for land, water, air and space vehicles. In general, the processing of glass sheets for use in the manufacture of transparencies for land and water vehicles usually include cutting a glass substrate to provide a glass sheet having a predetermined size; moving a bending iron having the glass sheet through a furnace to heat soften and shape the glass sheet; controllably cooling the shaped glass sheet to anneal or heat strength the shaped glass sheet, and using the shaped glass sheet in the manufacture of a transparency for a land or water vehicle. In general, the processing of glass sheets for use in the manufacture of transparencies for air and space vehicles usually include cutting a glass substrate to provide a glass sheet having a predetermined size; moving a bending iron having the glass sheet through a furnace to heat soften and shape the glass sheet; controllably cooling the shaped glass sheet to anneal the shaped glass sheet; cutting the shaped glass sheet to a second predetermined size; chemically strengthening the shaped glass sheet, and using the shaped glass sheet in the manufacture of a transparency for an air or space vehicle.
The difference between shaping a glass sheet for use with transparencies for land and water vehicles and shaping a glass sheet for use with transparencies for air and'space vehicles of interest in the present discussion is that the glass sheet for use with transparencies for land and water vehicles is cut to size before bending, whereas a glass sheet for use with transparencies for air and space vehicles is cut to an over size before bending and cut to size after bending. For purposes of clarity in the discussion of the glass window, the process for shaping a glass sheet for use with transparencies for land and water vehicles is also referred to as “cut-to-size”, and the process for shaping a glass sheet for use with transparencies in air and space vehicles is referred to as “cut-after-bend”.
The cut-to-size process is acceptable for making transparencies for land and water vehicles because the glass sheets are thinner, and the optical quality requirement for land and water vehicles is lower than the optical quality requirement for aircraft transparencies. More particularly, the thickness range for glass for automotive transparencies is in the range of 1.8 to 3 millimeters (“mm”) whereas the thickness range for glass for aircraft transparencies is in the range of 2 to 15 mm. Because the glass sheets used for making transparencies for air and space vehicles are thicker, the bending iron having the glass sheet remains in the furnace for a longer period of time to heat the sheet to its bending temperature, which usually results in marring or marking surface areas of the glass sheet in contact with the bending iron during the long heating periods. The marring or marking of the glass sheet can cause distortions on the surface of the glass sheets, which can make the optical quality of the glass unacceptable. Further, the displacement between the glass surface and the metal surface of the bending iron under the high temperature condition will also cause scratches in the glass surface, which results in unacceptable defects.
As can now be appreciated, the marring and marking of the glass in the vision area is presently reduced or eliminated by providing a bending iron and oversized glass sheet. After glass sheet is shaped, the shaped glass sheet is cut to size. The portions of the glass sheet cut away have the marring and markings from the bending iron.
As can now be appreciated it would be advantages to provide a bending iron to shape glass sheets for air and space vehicles that does not have the limitations of the presently available bending irons, e.g. but not limited to, a bending iron that does not cause surface defects, which causes optical distortions in the vision area of the transparency; a bending iron that can be used to make symmetric and asymmetric shaped glass sheets without having contact area distortions and scratches in the vision area of the transparency, and a bending iron that can be used in a cut-to-size process for shaping glass sheets to make transparencies for air and space vehicles.